1. Field of the Invention
This invention relates to an apparatus for converting a fixed bed pickup truck to a tilting bed truck, and more particularly, to a geometrically improved tilting mechanism for converting a fixed bed pickup truck to a tilting bed truck such that the relationship of the pickup bed to the passenger cab remains unchanged after the conversion.
2. Prior Art
The advantages of having a truck with the capability of selectively tilting the truck bed or hauling box to facilitate removal of materials transported thereon has resulted in a number of systems for providing such a feature. The systems heretofore used have been primarily of two types. The first is characterized by a truck bed hinged at the rear of the truck frame and tilted by the actuation of a hydraulic ram or other variable length arm connected directly between the forward end of the truck bed and truck frame. In order to accommodate the lifting ram and permit the truck bed to be positioned adjacent the truck frame when in the horizontal position, the lifting ram in these systems is normally exposed either within or without of the hauling bed, thus introducing the substantial disadvantage of having the lifting ram in an exposed position. Alternately, the lifting ram is positioned below the truck bed with the bed substantially raised above its normal designed position or with the ram so positioned as to introduce very inefficient leverage as it functions to tilt the truck bed.
A second type of lifting mechanism has been employed wherein a hydraulic ram is used to extend a multibar linkage consisting generally of two or three interconnected members. By unfolding the linkage, the truck bed is raised to the tilted position. Examples of this type of system are found in U.S. Pat. No. 3,617,090, issued to Samuel E. Huffman, and U.S. Pat. No. 3,043,629, issued to D. H. Schlueter, et al. In each of these configurations, the truck bed is tilted by extending the upper arm by use of a hydraulic ram acting between the lower arm and the upper arm.
Many of the prior art units have generally altered the relationship between the truck bed and the passenger cab thereby destroying the asthetic appearance of the vehicle. Moreover, the prior art systems have failed to disclose a simple conversion system which does not require extensive alteration to the truck frame or bed and which does not effect either vehicle structural or operating components such as the drive shaft, muffler and other original parts in converting the truck from a fixed bed to a tilting bed vehicle. While the multibar lift mechanisms introduce the advantage of the mechanism nesting below the truck bed, these tilting mechanisms fail to make the most advantageous use of unused space between the truck bed and truck frame which exists on many trucks now on the market.
Moreover, many of these units do not permit the conversion from a fixed bed to a tilting bed truck without alterations to the truck, and in many cases, the units can only be used, even with modifications to the truck, on a limited number of truck makes and models.